There could be a number of things at play here. First of all, the crazy little sound bites that Phaedra says are far more interesting than her saying how cute he is. A lot of the "normal" stuff could have been left on the cutting room floor. It was very telling last night the way she looked at his photos and was thrilled to catch the one of him smiling. Phaedra is a character, and the show is going to play that character up. Even Sheree, who does not seem like the type to go out of her way defending anyone, said on WWHL that Phaedra is far different than she comes off as on the show.
Another thing at play could simply be that is how Phaedra was raised. Her mom, like most moms, obviously loves Phaedra. She was, however, clearly a stern woman and her children were expected to tow a certain line. Phaedra still seems afraid to let her down, to the point of lying about when she got pregnant and sounding totally foolish in the process. Some parents don't dish out a healthy serving of hugs and praise, so maybe that isn't natural to Phaedra. It doesn't mean she doesn't have a natural maternal love for her son.